Predator Sleuthing

If you find an intact empty shell on the beach, chances are pretty good a starfish ate it. (It also might have died of disease or other natural causes, but that’s a whole different story).

Starfish use their hydraulic tube feet to pull the oyster apart, then they evert their stomach and digest the oyster remotely. Read about it here. They are voracious oyster eaters, and this one is particularly greedy.

If you find a shell with one edge clipped off, assume the perpetrator was a rock crab or a big dungeness:

If you find an oyster shell pockmarked with holes, a boring sponge probably helped bring about its demise. Boring sponges recycle calcium carbonate, a job that should become easier as ocean acidification weakens shells, facilitating the boring. Boring sponges are filter feeders and while they don’t actual eat the oysters, they do weaken the oysters, eventually causing death.

Here’s a photo of an oyster infested with boring sponge:

If you find a shell with a single hole bored into it, it was probably eaten by a some kind of drill snail. European drill snails, Japanese drill snails, and native drill snails are all found on our farm. Drill snails feast on small oysters (think baby Pacifics, or Olympias of all sizes). Moon snails are also drilling snails, but we’re not sure if they eat oysters. We know for sure that they eat the heck out of clams, however. The soft shell clam below just barely survived a moon snail attack:

And if you find a shell that’s been drizzled with garlic butter and then dumped in a midden, well… that’s a different story.